Have you been checked for bilesaltmalabsorption? I think that if you have problems with that you can get more problems with fat in the food. Not sure though. But I have IBS-D and that was one of the tests they tried on me. It was normal for me though. For me I follow the EFI diet, I try to keep my stress level under control since my IBS is highly influenced by stress, and I take loperamide (like Imodium) daily and that is really what makes it possible for me to have some sort of normal life.